Allison 1000

Allison 1000 Transmission Specs & Ratios

The Allison 1000 was first produced in 1999 by Allison Transmissions. In 2001, GM mated the Allison to its new 6.6L Duramax. The Allison 1000 is arguably one of the most desirable automatic transmissions in its category. Its popularity and excellent reputation can be attributed to its strength, reliability, and the technology applied to the transmission. In 2006, the Allison 1000 was converted from a 5 speed to a 6 speed automatic, making the later version a double overdrive. Not without flaws, the Allison suffers from lack of lubrication to the C3 clutch, while the C1 & C2 clutches are applied off center, causing uneven wear and often premature failure. The transmission is also known to lock into limp mode when owners begin adding performance enhancers to the Duramax diesel. Performance products, like programmers, push the Duramax beyond the transmission's limits and can cause excessive slippage, forcing the transmission to lock into 3rd gear. Regardless, the Allison is a true medium duty transmission with many desirable characteristics.